<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <script>

  let score=prompt('请输入分数')
    if (score>=90){
      alert('A')
    }
    else if(80>=score>=90){
      alert('B')

    }
    else if(70>=score>80){
      alert('C')

    }  else if(60>=score>70){
      alert('D')

    }
    else {
      alert('E')  
    }

  </script>
  
</body>
</html>